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Needing some AR-10 advice

These are groups from an AR-10 308 I’ve built. The load is custom 175 SMK over 41.6 Varget. Ive got it shooting pretty well but likes to throw one out almost every time. My first thoughts are inconsistent lock up going in or its coming out of battery a little soon some times??? I’m open to any discussion/ideas. I don’t think it’s me, I shoot a lot and some matches and my norm would be all five in the main group.
upload_2020-3-2_18-30-53.jpeg
 
Where does that flyer come in the string? First shot? Last shot? Somewhere in the middle? Is it consistent with placement and where it comes in the string? Does it settle in if it heats up or does it get worse?

A lot of variables when it comes to gas guns.
 
Where does that flyer come in the string? First shot? Last shot? Somewhere in the middle? Is it consistent with placement and where it comes in the string? Does it settle in if it heats up or does it get worse?

A lot of variables when it comes to gas guns.
It varies which is why I’m leaning to a lock up issue. The barrel has been seated to the upper so that’s tight.
 
When the round chambers, are your getting any bullet movement? A longer col , bullet moving forward. If there is a lot, more neck tension is needed, or as a last resort, a crimp.

Shorter col, bullet hitting feed ramp. Something else to check.
 
When the round chambers, are your getting any bullet movement? A longer col , bullet moving forward. If there is a lot, more neck tension is needed, or as a last resort, a crimp.

Shorter col, bullet hitting feed ramp. Something else to check.
I’m single feeding from a mag, releasing the BCG using the catch lever and letting the BCG slam home. I’m also running .001 taper crimp so there really shouldn’t be enough force to move the bullet but no I haven’t measured. Worth checking...and I am past mag length running about .015 jump at 2.855 COAL
 
When the round chambers, are your getting any bullet movement? A longer col , bullet moving forward. If there is a lot, more neck tension is needed, or as a last resort, a crimp.

Shorter col, bullet hitting feed ramp. Something else to check.
I just ran one through, clean feed, no damage, no dimensional change.
 
I have 2 ar10's. both are target rifles. may I suggest that you put the round on top of the mag, push it half way in the chamber, then release the bolt. get rid of the crimp. 2-3 thou neck tension will hold the bullet.
box stock ar10(t) shoots 1/2 and under at 100.
 
I have 2 ar10's. both are target rifles. may I suggest that you put the round on top of the mag, push it half way in the chamber, then release the bolt. get rid of the crimp. 2-3 thou neck tension will hold the bullet.
box stock ar10(t) shoots 1/2 and under at 100.
The Inconsistency of the seating die has been bothering me more the closer I get to match moa.
 
I've found similar issues, and I'd recommend the single load method above; or a bob sled to separate the mag feeding from rifle / ammo. If you don't see it when single loading, but you do when mag feeding; which it's a gas gun, so what's the point of single loading, it'll be time for mag tests.

You mention it's not consistently first or last round; could be follower or an uneven stack; could be a round moving forward in the stack this presenting forward vs. the others; could be your COL is too long and bullet tip is snagging on the mag. Mag springs make a difference too.

There's a lot to look at with how a magazine works and how rounds feed. Could even be as simple as a round that had an extra 30s of "cook" in a hot chamber.

Break it down into steps and try to keep consistent. Is it a round that is always an even or odd number? (Feed ramp right/left?)

I'd say try a few things, but the booger is that if it fixes it; what was the problem to avoid?

I'd start with full mags every time, try a few brands / styles of mags, and take good detailed notes on all of the above.

-Mac
 
Let the bolt go forward a little before releasing it. The spring on the AR-10 is very strong, and if you're single loading, you don't need all of that force, maybe release the bolt from 1/2 open position. As mentioned before, place the bullet part-way into the chamber, and don't load it in a magazine. However, I would recommend placing the round on top of the mag, then pushing it in using the bolt release. Then bring the bolt back a couple of inches before releasing it. Never get a finger in the loading port of an AR-10. If the bolt closes, that finger will bring an end to your shooting for the day.
 
Sometime for 5 shot groups flyers are not actually flyers. If you keep shooting more and more shots into the group you will find that the flyers are really just part of the group.
 
For tonight's test I've removed one standard buffer weight and installed one heavy carbon steel buffer weight. I'll do everything the same as I have been for consistency.
 
It is kind of a light load of Varget for the bullet weight. Have you worked up this load or was it just recommended?

How far out is the brass being thrown? If it is tossing the brass a long distance I would recommend an adjustable gas block and tune it to reliably toss the brass a foot or two from the gun.
 
explain that statement
tip to base will nearly always vary because production bullets vary.
what you want is ogive to base to be consistent. Hornady tool or similar.
It's not a micro adjustable die which is what i use on all my other match loads. So the seating depth at this time is +- a couple thousandths and measured COAL. Not enough to make a difference in 100 yard testing but will need refined as I get the group tightened and develop it out to my 600 yard 1/2 moa goal.
 
It is kind of a light load of Varget for the bullet weight. Have you worked up this load or was it just recommended?

How far out is the brass being thrown? If it is tossing the brass a long distance I would recommend an adjustable gas block and tune it to reliably toss the brass a foot or two from the gun.
Its a load Ive picked from the middle of a velocity ladder with a flat spot of .6 grains. It's the best 1/10 in the flat spot. On the slow side for sure but this is a new gun that I want to see group before I start pushing velocity. Ive had it to the next higher node and dont like what I see on the primers and cases.
 
Get a bob sled, single feed, allow alittle time between shots. Dont let the round warm up in the chamber. Do some slow firing and see if that makes any difference.

You dont need a crimp, just enough neck tension to hold the bullet in place.

Brass prep does make a noticeable difference in ARs too, done it, still do it.

How much play is there between your upper and lower? If there is any movement that will cause this issue. The fix is shims. I posted a a big something about AR accuracy while back, if you can find it its worth a read. Its jmo, but its worked for me and Ive yet to see an AR outshoot mine. Several tips and tricks to play with. Theres so many could be issues you just gotta start from building it and pull every trick in the book to feel satisfied you remedied things.

Square receiver face, torques on everything, run it wet, gas flow, how clean is it, trigger, shims, your rest, your grip plays a factor shooting, list goes on.
 
Get a bob sled, single feed, allow alittle time between shots. Dont let the round warm up in the chamber. Do some slow firing and see if that makes any difference.

You dont need a crimp, just enough neck tension to hold the bullet in place.

Brass prep does make a noticeable difference in ARs too, done it, still do it.

How much play is there between your upper and lower? If there is any movement that will cause this issue. The fix is shims. I posted a a big something about AR accuracy while back, if you can find it its worth a read. Its jmo, but its worked for me and Ive yet to see an AR outshoot mine. Several tips and tricks to play with. Theres so many could be issues you just gotta start from building it and pull every trick in the book to feel satisfied you remedied things.

Square receiver face, torques on everything, run it wet, gas flow, how clean is it, trigger, shims, your rest, your grip plays a factor shooting, list goes on.
I'm no stranger to pulling extreme accuracy from an AR-15 but this is my first 10. I really appreciate everyone taking the time and effort to throw their ideas out but pretty much what has been addressed in everything above is what I'd consider common information and accuracy tricks we've all figured out along the way. I keep hoping someone will discuss the gas system/bcg/lock up as it relates to accuracy mostly because my gut feel is that I have a gremlin in that area and know very little about how to define and resolve issues there.
 

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